Gaskets are often used as a seal between mating metal surfaces. One common application involves the placement of a gasket between a head and an exhaust manifold of an internal combustion engine. Another application involves gasket placement between the exhaust manifold and an exhaust pipe flange. Gaskets for either application can be considered high temperature gaskets and more particularly exhaust manifold gaskets since they provide an exhaust seal which prevents the byproducts of combustion exiting the engine from escaping into the engine compartment of a vehicle.
Exhaust manifold gaskets are typically installed by placing the gasket between an exhaust manifold and its mating component and aligning bolt holes or apertures formed in the gasket with corresponding holes formed in the manifold and mating component. A threaded fastener passes through the manifold and gasket and engages a corresponding threaded aperture formed in the mating component. Some maneuvering of the manifold and gasket relative to the mating component may be required to align the holes therein with the corresponding threaded apertures of the mating component before the fasteners can be inserted.
There are problems in such an assembly process. In particular, the gasket may slip from its desired position or drop off the end of the inserted fastener before it can be fixed in place between the exhaust manifold and its mating component. It would be highly desirable to have a gasket that will not fall off the threaded ends of the fasteners after they have passed through the holes formed in the gasket. Thus, an assembler could more easily maintain the gasket in position relative to the manifold when mating it to its mating component.
Several methods are known for capturing the threaded ends of fasteners, but they are ill suited for a high temperature gasket. One approach is to provide a star shape opening defining inwardly directed fingers in a soft gasket material. Pushing a threaded fastener through the gasket opening causes the fingers to open outwardly in the direction of fastener motion, partially engaging the fastener. The gasket material around the fastener is compressed upon assembly completion to provide a seal around it. Use of this configuration with a metallic high temperature gasket would be problematic because the high bending strength of metal resists bolt insertion and the resultant axially extending fingers prevent the manifold and its mating component from being drawn together to form the desired seal.
Retention means in gaskets have also been employed to fix a gasket over locating pins. For example, an aperture in the gasket has radially extending fingers which engage the pin. As the gasket is pushed down over the pin, the fingers deflect upwardly, locking the gasket to the pin. One difficulty with such an approach as applied to threaded fasteners is that with the fingers so engaging the fastener, the torque required to turn the fastener is undesirably increased. Another difficulty is that such a retention means may damage the fastener threads.
Finally, it is known to form specialized holes in the gasket which capture a threaded fastener. The holes require the use of specialized fingers with an inner diameter greater than a corresponding minor thread diameter and smaller than a corresponding major thread diameter. Such fingers require extremely high tolerances, increasing manufacturing cost. Further the use of the fingers can be easily compromised by inadvertent and not easily detected component misalignment during gasket assembly.